This application relates to U.S. Pat. No. 4,797,928 issued Jan. 10, 1989 to John Dyke.
This invention relates to cryptographic devices and more particularly to an improved encryption printed circuit board.
Various systems have been developed in the prior art for enciphering digital information to improve the security and privacy of data within data processing systems, during transmission over telecommunications networks, and during storage on media such as magnetic tape and disk. Examples of such cipher systems may be found in U.S. Pat. Nos. 3,798,359 and 3,958,081.
In known cipher systems the bits of the information to be enciphered are rearranged or replaced by substitute bits under control of a secret cipher key. To decipher the enciphered operation the substitution is reversed. Enciphering methods have been combined to provide secure ciphers. For example, the bits have been transposed prior to substitution, groups of bits have been substituted, combining using exclusive OR, and these techniques have been altered several times during the enciphering and deciphering process. Such cipher systems are practically unbreakable without testing all possible keys and the key can be made large enough to make such testing prohibitively time consuming.
Thus, for piracy to be profitable access to the key is necessary. Various systems have been devised to keep the key from being accessed through the computer. Such systems have included separating the enciphering system from the computer wherein the computer calls for information and gets the results only.
The essential difference between the known prior art devices and the invention of U.S. Pat. No. 4,797,928 is the provision of an encryption printed circuit which is an IBM half-sized printed circuit board with complete interface to a card reader. The technique used by the encryption printed circuit is known as the National Bureau of Standards Data Encryption Standard (DES) whose DES function is provided by a low cost, high performance integrated circuit having a microprocessor which automatically handles many of the DES functions. The use of the microprocessor unburdens the host system which provides greater transfer speed of information and increased security of the information.
Differences between the known prior art devices and the related invention of U.S. Pat. No. 4,797,928, and the present invention are the elimination of essentially all handshaking between the host computer and the ciphering printed circuit board; that is through the use of a dual port random access memory (DPR) only 1 byte in software is required after a connection is established between the two communicating devices, and the provision of an "audit trail" for determining who accesses the encryption printed circuit board, the time and date of access and how long the encryption printed circuit board is accessed.